In the past, photographic film cartridges disclosed in U.S. Pat. No. 5,251,840 and Japanese Unexamined Patent Publication No. 5-45801 have been known as photographic film cartridges capable of feeding photographic film stowed in a cartridge when the photographic film cartridge is loaded in a camera.
In the conventional photographic film cartridge, flanges molded using a flexible raw material are engaged with both ends of a spool, about which photographic film is wound, within the cartridge. Juts of annular tongues molded unitedly along the margins of the flanges are used to wrap part of the outermost circumference of the photographic film wound about the spool from both ends of the film. Thus, loose wind of photographic film is prevented.
When the spool is rotated in a feed direction, the photographic film rotates together with the spool without being wound loosely. In the vicinity of a film port of a cartridge body, the photographic film is fed outside while thrusting the juts in a film-width direction.
The details of the structure of the foregoing conventional photographic film cartridge, and the film feed operation will be described in conjunction with the sectional view of a cartridge of FIG. 7 and the view showing a film feed path of FIG. 8 in which a camera in which film feed is under way is viewed from behind.
In a cartridge 101, photographic film 102 is, as shown in FIG. 7, stowed in a cartridge body 101a and wound about a spool 103 in the cartridge body 101a. Flanges 105 and 106 molded using a flexible raw material are respectively engaged with opposite ends of the spool 103 in the cartridge. Annular juts 105a an 106a, for preventing loose winding of the film 102, are formed unitedly along the outer margins of the flanges 105 and 106.
The film 102 fed from the cartridge 101 having the foregoing structure to a camera passes, as shown in FIG. 8, behind a photographic aperture 108 of the camera and is then wound about a spool 107 in the camera. At this time, the annular juts 105a and 106a of the flanges 105 and 106 are elastically deformed to be thrust in a width direction of the film in the vicinity of a film port 104 by means of the film 102. The annular juts 105a and 106a thus apply respectively pressing forces F and F' to the film. The deformed portions of the juts 105a and 106a are denoted by reference numerals 105b and 106b. A perforation 102a is formed by piercing the film 102 at given intervals along one edge of the film 102 in the width direction thereof.
When the conventional photographic film cartridge 101 is employed in a camera, as mentioned above, the film 102 receives the pressing forces F and F' resulting from elastic deformation of the flanges 105 and 106 in the vicinity of the film port 104. If the camera is left intact in this state for a long period of time, the film 102 undergoes deformation, which disables the film from being reset soon, because the pressing forces F and F' have operated on the film for the aforesaid long period of time.
FIGS. 9 and 10 show a section of the film in the width direction thereof. FIG. 9 shows the section of the film in a normally curled state in which the film does not receive the pressing forces F and F'. FIG. 10 shows a curled state of the film after the film has received the pressing forces F and F' shown in FIG. 8 for a prolonged period of time.
In FIGS. 9 and 10, the emulsion-coated side of the film 102 is denoted by reference numeral 102b. In general, the photographic film 102 has a curling characteristic that the emulsion-coated side 102b becomes concave. As shown in FIG. 9, the magnitude C1 of a curl in the normally deformed state is within a given range. As shown in FIG. 10, the emulsion-coated side 102b of the film 102 having received the pressing forces F and F' for a prolonged period of time also becomes concave. However, a large curl of a magnitude C2 exceeding the aforesaid given range occurs.
FIGS. 11 and 12 are views showing an 11/12-11'/12' section of an aperture shown in FIG. 8. FIG. 11 is a sectional view showing a state in which, when film in the normal deformed state shown in FIG. 9 is fed, the film 102 in the photographic aperture 108 is leveled by a platen 110. FIG. 12 shows a state in which after the camera is left intact for a long period, when a deformed region of the film corresponding to the next frame 102c (See FIG. 8), which has been deformed due to pressing, reaches the photographic aperture 108 with one-frame wind, the deformed region of the film 102 in the photographic aperture 108 is leveled by the platen 110.
As shown in FIGS. 11 and 12, a pair of known film rail planes 109a and a pair of known platen rail planes 109b are located above and below the photographic aperture 108 formed in a camera body 109. The platen 110 for pressing the film is pressurized to come into contact with the platen rail planes 109b.
The emulsion-coated back side of the film 102 in the normal state shown in FIG. 9 is substantially in contact with the platen 110 within the photographic aperture and retains a relatively good flat state. Even if the film 102 warps relative to the platen 110 due to deformation caused by a difference of the film 102 from another film or a change of use environments, as shown in FIG. 11, the magnitude Z1 of the warp is within a range equal to or smaller than, practically, substantially 0.02 mm.
However, when a curled portion that has received the pressing forces F and F' for a long period of time and deformed greatly is pressed by the platen 110 and thus leveled, the center curl is greatly repulsed from the platen 110. The film 102 juts out by a significant amount in a forward direction of the camera from the platen 110 as shown in FIG. 12.
As a practical example, an example, in which the pressing forces F and F' are set to about 30 g, and the film 102 in which a polyethylene naphthalate of about 0.09 mm thick is used as a film base material is left intact (in the position shown in FIG. 8) for 24 hours, will be described. Immediately after the film is wound by one frame in the pressed state, the magnitude Z2 of a warp in the center of the film on which the pressing forces operate ranges from 0.03 to 0.10 mm.
When photography is performed in this state, since the image formation side of a lens and the sensitized side of the film are mismatched greatly along an optical axis in the center of a picture area, a photograph that is out of focus is taken.
The present invention attempts to solve the foregoing drawback. An object of the present invention is to provide a camera to which a photographic film cartridge of a feed type in which pressing forces working in a width direction operate on photographic film is adaptable, and in which even after the photographic film is left intact in the camera for a prolonged period of time, the influence of deformation occurring in the film is limited and in-focus photography can be achieved.